Figure 2 Variations in solar total radiation incident on the Earth, in watts per square meter, on different time scales. (a) Recorded, day-to-day changes for a period of seven months at a time of high solar activity. The largest dips, of up to 0.3%, persist for about a month and are the result of large sunspot groups that are carried across the face of the Sun with solar rotation. (b) Observed changes for the fifteen-year period over which direct measurements have been made, showing the 11-year (Schwabe) cycle of amplitude about 0.1 percent. (c) A reconstruction of variations in solar radiation since about 1600, based on historical records of sunspot numbers and postulated solar surface brightness during the 70-year Maunder Minimum. Estimated variations are of larger amplitude than have yet been observed. (d) A longer record of solar activity based on postulated changes in solar radiation that are derived from measured variations in 14C and 10Be.